1. Field of the Invention
The present invention relates to a scrubber for cleaning gases, in particular to a scrubber in the form of a tower containing several scrubbing stages.
2. Description of the Related Art
Scrubbers are common in the context of cleaning gases, and they are used for, among other applications, cleaning exhaust gases, fumes and other process gases in, for example, the chemical industry. The scrubber is used to clean the gases from contaminants that should not be released into the atmosphere.
A scrubber is normally designed as a vertical cylinder, in which a process fluid circulates, normally in a counterflow direction to the gas that is to be cleaned. The process fluid, such as water with or without additives, is pumped around and injected into the scrubber through a nozzle system in the upper part of the scrubber. The gas that is to be cleaned is introduced at the bottom of the scrubber, and is subsequently allowed to rise, in order to leave the scrubber at its top. The process fluid and the gas are in this way brought into contact with each other, whereby certain components that are present in the gas, such as, for example, HCl, SO2, and HF, are absorbed in the process fluid. The gas is in this way cleaned from contaminants.
In order to improve the contact between the process fluid and the gas that is to be cleaned, what is known as column packing may be installed in the scrubber. The column packing may be manufactured from plastic or a metallic or ceramic material, and it may be designed with various geometrical forms in order to offer a greater or lesser contact area between the gas and the fluid.
A scrubber can, as has been mentioned above, be built in several individual stages, where each stage has its own pump circulation circuit and its own nozzle system. The stages are in this case separated by special separation layers that collect the process fluid and lead it onwards to a pump tank from which process fluid can, in turn, be led onwards to the pump circulation system. The pump tank must be able to accommodate a volume of fluid that is sufficiently large such that it can offer satisfactory function of the pump system during normal operation, and, most importantly, during start-up and shut-down sequences when all fluid is to be collected in the tank.
In a scrubber that has only one stage, the lower part of the scrubber, the bottom part, acts as pump tank. In scrubber systems with two or more stages, a separate tank volume is required for each stage of the scrubber, such that the fluids from the various stages are not mixed with each other. The traditional manner of constructing this has been to have an external tank located at a lower level than the scrubber stage.
With scrubber systems having several stages and with the scrubbers placed in a tower, the solutions described above with the tanks lead to extensive pipe-laying, for both the supply and withdrawal lines for each scrubber. Since towers with several scrubber stages can be very high, severe demands are placed on the pumps that are to circulate the process fluid, such that they can pump fluid to the height that is required for large volumes. Furthermore, the fluid content of the pipes becomes very large, and the tanks must be dimensioned such that they can accommodate all the fluid when the flow is stopped for one reason or another.
It is therefore a purpose of the present invention to achieve a scrubber, in particular a scrubber tower with several scrubber stages, in which the problems described above with the laying of pipes and tanks can be solved in a more efficient manner.